The unique feature of this device lies in its integration of a true color non-mydriatic fundus camera, in addition to the spectral-domain OCT. Besides being a cost and space saving option, this setup makes the correlation of specific lesions observed on the color fundus photo to the corresponding OCT image possible.

Various overlays, such as the topographic retinal thickness map and projection image, may be placed over the fundus photo simultaneously with different fundus grids, such as the EDTRS-like map, rectangular map 5 mm x 5 mm map with six boxes horizontally and vertically and volume map.

The superposition of the retinal thickness map with the EDTRS-like map helps to detect eccentric fixation See Figure 3 , which can then be corrected manually.

In addition, the 3D OCT software interfaces smoothly with IMAGEnet and integrates with other types of images like fluorescein and indocyanine green angiography, red-free and autofluorescence and thus it is possible to register fluorescein and other image types and register them to OCT scans.

Bioptigen 3D SDOCT is a device clinically suitable for the scanning of patients, in addition to its usefulness in clinical and animal biomedical research.

The device is unique in that it has two light sources, one centered at 1, nm and another at nm. The dual light source makes it especially suitable for multiple research settings.

The 1, nm engine may be clinically helpful for anterior segment imaging and in basic scientific research for tissue, small animal, external and ex-vivo imaging.

The nm engine may be clinically helpful for human retinal imaging and in basic science research for retinal imaging in small i. A nm bandwidth light source upgrade is also available for high-resolution imaging.

Additionally, the Bioptigen 3D SDOCT contains a variety of scanners and probes for various applications such as a Doppler processing system for retinal blood flow analysis, small animal probe for basic scientific research, pediatric probes for infants and corneal probe for anterior segment examination.

It utilizes a SLD light source at nm. The design of the Cirrus is different from the other commercial OCT devices since it is not designed around a slit lamp and joystick, but instead employs a mouse.

Additionally, the Cirrus has a dedicated iris CCD charge-coupled device camera that allows for live monitoring of the pupil during scans and a separate near infrared fundus SLD camera nm for live fundus visualization.

For repeat scans, Cirrus HD-OCT has a "repeat function," whereby with a click of a mouse, the device returns to the previous setup for that particular patient head and chin rest positions and camera focus and it activates visit-to-visit registration using retinal vessel tracing.

The use of vessel registration is an improvement from older generation devices, as it does not rely merely on the proper patient fixation, thus improving inter-scan reproducibility.

The use of registration is also useful for tracking the progression of various ocular diseases. This function allows for visualization of pathologies such as epiretinal membranes or macular holes.

With the Cirrus HD-OCT the operator can also create customized scan patterns by varying the raster length or scan density and changing the angle of the raster lines.

The system uses SLD light source centered at nm. The rapid scanning speed decreases scan time and further reduces instances of fixation drift and motion artifacts, while expanding retinal coverage.

The improved resolution theoretically allows for the visualization of even higher level of detail. Copernicus HR also has a Doppler analysis module to allow for the examination of the retinal vascular system, and allows for analysis such as flow velocity estimation, and velocity distribution mapping.

One advantage of the RTVue is its innovative method of image acquisition. The RTVue acquires images in real time, which is particularly useful in patients who are prone to inattention, fixation losses or blinking during scans.

Because the software allows the operator to view sets of images taken at different periods of time immediately, it maximizes the opportunity to obtain the highest quality OCT images.

Another one of RTVue's strengths lies in the wide number of available scan protocols. This diversity provides users in both research and clinical settings multiple ways to view and analyze the retinal layers and optic nerve.

For example, EMM5 is the RTVue's primary macular mapping scan— it utilizes a grid-like scanning pattern with an outer 6 mm x 6 mm area with 13 horizontal and 13 vertical scans of 0.

This pattern allows for visualization of even finer details closer to the center of the fovea and creates accurate retinal thickness maps since little interpolation of points is needed.

The EMM5 also has the ability to create full retinal, inner and outer retinal thickness maps Figure 5 A. The wide 6 mm x 6 mm scan area of the protocol provides a high degree of freedom for the operator to reposition the 5 mm-diameter Early Treatment of Diabetes Retinopathy Study-like map in cases of fixation drift.

Registration via vessel tracing is also available. The RTVue has an option for an anterior chamber attachment lens, which allows for examination of the cornea and the anterior chamber.

In addition to OCT, this device also has a confocal scanning ophthalmoscope which uses the same optics as the OCT scanner. Confocal SLO generates the fine surface detail of the fundus, while the OCT C-scan enface view of a series of sequential OCT scans down the fundus put together provides the details for the retinal layers.

Thus, this system registers scans point-to-point in real time. The data are mapped onto the confocal SLO fundus image and may be also mapped onto the retinal thickness map.

In this way, one can assess the relationship between retinal function and structure at particular points in the retina. HRA Heidelberg Retinal Angiography uses infrared confocal laser scanning for digital acquisition of fluorescein angiography and indocyanine green angiography with 3D resolution.

This system allows for up to six different imaging modalities including spectral-domain OCT, fluorescein angiography, indocyanine green angiography, fundus autofluorescence, red free and infrared photography See Figure 6.

The relative high price of the Spectralis due to the various optional factures that may be added onto the core unit consisting of two imaging modes: SD OCT and infrared photography presents as a potential disadvantage, but the base units alone are also available.

The light source used is SLD centered at a wavelength of nm. The Spectralis utilizes a dual-beam scanning system consisting of a confocal SLO reference beam to acquire reference scans for eye movement tracking and guides a second beam to simultaneously acquire OCT images.

The eye-tracking technology recognizes the presence of eye movement then repositions the scan pattern and discards scans with motion artifacts.

The Spectralis uses registration by retinal structures to allows for automatic rescan of the retina at the same location as the previous visit, eliminating subjective scan positioning by the operator and thus precise longitudinal tracking of various retinal diseases such as wet age-related macular degeneration is possible.

In the presence of perimetric disease, finding RNFL bundle loss on SD-OCT with a corresponding abnormality in the visual field served by those retinal ganglion cells can help confirm the diagnosis of glaucoma.

Studies have evaluated the reproducibility and repeatability of SD-OCT measures relevant to assessing change over time.

The intervisit tolerance limit for average RNFL thickness was 3. However, it is important to exclude any scans that are not of adequate quality.

Scans with a signal strength less than 6, with eye movement or blinking artifacts within the 1. Glaucoma progression algorithms can be divided into event-based and trend-based approaches, similar to visual field progression detection methods.

Event-based analysis defines progressive change when a follow up measurement exceeds a pre-established threshold for change from baseline.

Alternatively, trend-based analysis defines progression by monitoring the change over time using regression analysis to provide a rate of progression and corresponding significance level.

Due to the variability or possible artifacts with SD-OCT measurements, all changes on OCT should be correlated with visual field changes before confirming definite progression.

When such correspondence is not found, caution should be exercised and sources of erroneous measurements should be sought, a few of which are reviewed below.

The normative database for the Cirrus SD-OCT consisted on healthy individuals with an age range between 18 and 84 years mean of The refractive error ranged from One common special case is the myopic patient.

As mentioned previously, high myopes were not included in the normative database. Myopic eyes have thinner RNFL measurements, which can confound comparisons to the normative database.

Additionally, myopic eyes can have unique distributions of RNFL bundles. With increasing myopia, the superotemporal and inferotemporal RNFL bundles tend to converge temporally.

Due to this shift, although the peaks are of normal magnitude, they can be interpreted as thinned due to having a different distribution from the normative database.

Additionally, even in normal eyes, split RNFL bundles, both superiorly and inferiorly, have been found on histologic section, thus representing a true normal variant which may appear abnormal on SD-OCT see figure 7.

When assessing the adequacy of a scan, the signal strength should always be noted. The signal strength, reported on a scale of 0 to 10, is defined as the averaged intensity value of the signal pixels in the OCT image.

Lines should not come together go to zero. Occasionally, one will find that the segmentation lines are misplaced along the retina leading to errors in the calculation of RNFL thickness see figure 9.

These segmentation errors are more common in the presence of poor signal strength, tilted discs, staphylomas, large peripapillary atrophy, epiretinal membranes, and posterior vitreous detachments.

The longer the eye, the thinner the RNFL, and the smaller the optic disc area and neuroretinal rim area. However, refractive error independent of axial length has not been found to affect RNFL thickness measurements as long as a well focused fundus image is obtained during scan acquisition by utilizing the Cirrus SD-OCT internal fixation focus adjustment.

SD-OCT is a powerful objective structural assessment tool that can greatly assist clinicians in diagnosing and managing glaucoma especially early disease , when used in conjunction with visual field testing and serial clinical exams.